IF you had used summons during the fight with Jon Irenicus at the Tree of Life, you will not be able to rest in Hell because, surprise! Surprise! The game still thinks you are engaged in battle with J.Irenicus and you will see battletext between your summon and J.Irenicus who will not fight back.
And of course, this means you cannot rest because the game thinks you're still engaged in battle.
As a result, I never used summons again to fight J.Irenicus at the Tree of Life.
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If not a Sorcerer, then a Paladin.
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Baldur's Gate Item Mart